Process for operating an internal combustion engine, in particular of a motor vehicle

ABSTRACT

An internal combustion engine, in particular for a motor vehicle, that is provided with a control unit for controlling and/or regulating the power output by the internal combustion engine as a function of performance quantities of the internal combustion engine and, in particular, as a function of a driver request is described. A permissible variation in output power over a predetermined period of time and an actual variation in output power over a corresponding predetermined period of time can be determined and compared to one another by the control unit.

DESCRIPTION

The present invention relates to a method for operating an internalcombustion engine, in particular for a motor vehicle, in which the poweroutput by the internal combustion engine is controlled and/or regulatedas a function of performance quantities of the internal combustionengine and, in particular, as a function of a driver request. Thepresent invention also concerns an internal combustion engine, inparticular for a motor vehicle, having a control unit for controllingand/or regulating the power output by the internal combustion engine asa function of performance quantities of the internal combustion engineand, in particular, as a function of a driver request.

A method and an internal combustion engine of this type are known, forexample, from German Patent Application 1 96 09 242. According to thispublication, the performance quantities of the internal combustionengine are determined with the help of a multiplicity of sensors andsupplied to an electronic control unit. The latter processes theperformance quantities and activates a multiplicity of actuators, suchas the injection valves and spark plugs of the internal combustionengine, as a function of these performance quantities. The power outputby the internal combustion engine is controlled and/or regulated in thismanner to the value desired, in particular, by the driver.

It is possible for sensors, in particular, to demonstrate measuringerrors, for example due to aging phenomena. The consequence of this isthat the entire control and/or regulation action of the internalcombustion engine becomes susceptible to errors over time and no longercorresponds to the value desired by the driver.

For example, if an air-flow meter provided in the intake manifold of theinternal combustion engine generates an incorrect output signal, thiscan lead to an excessive amount of fuel being injected into thecombustion chamber of the internal combustion engine. This causes theinternal combustion engine to generate a power that is much higher thanthe power desired by the driver.

In the above-mentioned German patent application, a monitoring system isprovided that is used to continuously compare the power actually outputby the internal combustion engine to a permissible power. Thepermissible power is detected, for example, on the basis of theaccelerator position, i.e., on the basis of the power desired by thedriver. If the actual power of the internal,combustion engine exceedsthis detected permissible power, a sensor error is concluded.Appropriate action can thus be taken, in particular to correct theerror.

It is known that, due to tolerances, different sensors of the same typefrequently generate different output signals under the same conditions.In the monitoring system described according to German PatentApplication 1 96 09 242, these tolerances of the input sensors mustadditionally be taken into account when detecting the actual andpermissible power. As a result, the monitoring system detects only amajor sensor error as being impermissible.

The object of the present invention is to provide a method for operatingan internal combustion engine in which even minor sensor errors aredetected early on.

This object is achieved according to the present invention with a methodof the type mentioned in the preamble and an internal combustion engineof the type mentioned in the preamble in that a permissible variation inoutput power over a predetermined period of time and an actual variationin output power over a corresponding predetermined period of time aredetermined and compared to one another.

Thus, instead of monitoring the actual and permissible power of theinternal combustion engine as absolute quantities, the method accordingto the present invention uses the variations in these absolutequantities, i.e., relative quantities, for monitoring purposes.According to the present invention, therefore, the variations in theactual and permissible powers, respectively, of the internal combustionengine are determined over a certain predetermined period of time. Thesevariations, i.e., the relative quantities, are then compared to eachother and, as a function of this comparison, action is taken as neededto correct the error.

In sensors of the same type, the tolerances of the individual sensorshave an influence only on their absolute output signals. As previouslymentioned in the preamble, these absolute output signals can thereforealso vary among different sensors of the same type under the sameconditions. However, it can be assumed that the variations in outputsignals, i.e., their relative quantities, remain essentially more orless the same in all sensors of the same type. In particular, theserelative quantities remain more or less the same over a predetermined,preferably relatively short, period of time.

In other words, this means that the output signals of different sensorswithin the same sensor type vary in more or less the same way under thesame conditions and over the same period of time. The sensor tolerancesare therefore no longer a factor when using the relative quantities,i.e., when comparing the variations in the actual and permissible powerof the internal combustion engine over the same predetermined period oftime.

This means that the sensor tolerances no longer have to be taken intoaccount, and thus smaller, in particular abrupt, sensor errors can evenbe detected. In particular, it is possible according to the presentinvention to detect the relative quantities, i.e., the actual andpermissible variations in power output by the internal combustionengine, much more accurately without considering the tolerances than waspreviously possible with the absolute quantities of the actual andpermissible power. This results in the above-mentioned advantage thateven smaller variations, and thus smaller sensor errors, can be detectedand indicated.

In advantageous embodiments of the present invention, the permissiblevariation in output power over the predetermined period of time isdetermined as a function of the speed of the internal combustion engineor the driver request, in particular as a function of the variation inthe position of an accelerator. These actions have proved to beparticularly simple and yet accurate means for calculating thepermissible variation in the power output by the internal combustionengine.

In a further advantageous embodiment of the present invention, theactual variation in output power over the predetermined period of timeis determined as a function of the oxygen content of the emitted exhaustgas and/or as a function of the intake air flow. These actions haveproved to be particularly simple and yet accurate means for calculatingthe actual variation in the power output by the internal combustionengine.

It is particularly suitable if an error signal is generated if theactual variation in output power over the predetermined period of timeis greater than the permissible variation in output power over the samepredetermined period of time. This makes it possible to switch theinternal combustion engine to an emergency mode, if necessary, or toalert the driver to the error and/or to take, some other action tocorrect the error.

In one advantageous :embodiment of the present invention, theperformance quantities acting upon the internal combustion engine areconverted: to torques, in particular to a permissible and an actualvariation in a torque output by the internal combustion engine.Especially in the case of torque-driven internal combustion engines, andparticularly in the case of lean-mix engines or engines with direct fuelinjection, this has proven to be an especially effective means ofmonitoring the sensors.

It is especially important to implement the method according to thepresent invention in the form of an electric storage medium that isprovided for a control unit of an internal combustion engine, inparticular for a motor vehicle. On the electric storage medium is storeda program that can run on an arithmetic unit, in particular on amicroprocessor, and is suitable for carrying out the method according tothe present invention. In this case, therefore, the present invention isimplemented by a program stored on the electric storage medium so thatthis storage medium provided with the program is equally representativeof the present invention as the method which it is suitable to carryout.

Further features, applications, and advantages of the present inventioncan be derived from the following description of embodiments of thepresent invention, which are illustrated in the drawing. All describedor illustrated features form the object of the present invention, eitherby themselves or in any combination, regardless of their combination inthe patent claims or their references as well as independently of theirformulation and depiction in the description and in the drawing,respectively.

The one FIGURE in the drawing shows a schematic block diagram of oneembodiment of a method according to the present invention for operatingan internal combustion engine.

The FIGURE shows an internal combustion engine 1 that is provided with acombustion chamber containing a piston. In addition, an injection valveand a spark plug are assigned to the combustion chamber. If fuel isinjected by the injection valve into the combustion chamber, and if thisfuel is then ignited by the spark plug, the resulting combustiontransmits a torque to a crankshaft via the piston. As a result, thecrankshaft turns, causing internal combustion engine 1 to output power.

Internal combustion engine 1 is provided with a multiplicity of sensors,including an air-flow meter 2, an exhaust gas sensor 3, and a speedsensor 4.

To internal combustion engine 1 is assigned an electronic control unitthat is used to control and/or regulate, in particular, the combustionof fuel in the combustion chamber of internal combustion engine 1. Forthis purpose, the control unit is provided with; a microprocessor thatcontains a stored program in a storage medium, in particular in aread-only memory, with this program being suitable to perform the entirecontrol and/or regulation action.

Input signals that represent performance quantities of the internalcombustion engine measured by sensors are applied to the control unit.Among other things, the control unit is connected to air-flow meter 2,exhaust gas sensor 3, and speed sensor 4. The control unit is alsoconnected to a pedal sensor 5 that generates a signal indicating theposition of an accelerator that can be operated by a driver.

The control unit generates output signals that can be used to influencethe performance of the internal combustion engine via actuators,depending on the desired control and/or regulation action. For example,the control unit is connected to the injection valve and spark plug andgenerates the signals needed to activate them.

Based at least on the signals generated by pedal sensor 5 and speedsensor 4, the control unit calculates, in a block 6, a maximumpermissible variation in the torque output by internal combustion engine1 over a predetermined period of time. For example, the control unitcalculates a maximum permissible torque variation of this type for aspecific period of time lasting, for example, 1/10 second. The controlunit thus determines the maximum amount by which the torque output byinternal combustion engine 1 can vary, based on the accelerator positionand speed of internal combustion engine 1 and possibly based on thevariations of these quantities over this period of time.

Because the new torque should not begin, for example, until theaccelerator position changes, the variation in torque also occurs lateron and is thus delayed. This delay is dependent, for example, on thespeed of internal combustion engine 1.

In a block 7, the control unit calculates an actual variation in thetorque output by the internal combustion engine over a correspondingpredetermined period of time, based on the signal generated by exhaustgas sensor 3 and/or air-flow meter 2. The control unit thus determinesthe maximum amount by which the output torque of internal combustionengine 1 has actually varied, based on the exhaust gas oxygen contentand/or the intake air flow and possibly based on the variations of thesequantities over the specified period of time.

The determination of the maximum permissible and actual torquevariations, respectively, is always related to the predetermined periodof time. The permissible and actual torque variations therefore do notrepresent absolute quantities, but rather relative quantities per timeperiod.

The permissible and actual variations in the torque output by internalcombustion engine 1 are compared to one another in a block 8. Therefore,the permissible and actual torque variations per time period arecompared to one another. In doing this, the above-mentioned delay istaken into account. This means that a calculated maximum permissibletorque variation is compared to a delayed actual torque variation, i.e.,one that occurs at a later point in time.

If the actual variation in the torque output by internal combustionengine 1 is smaller than the maximum permissible variation in the outputtorque, this means that the sensors involved in controlling and/orregulating internal combustion engine 1 are essentially in properworking order. It also means that the control unit itself is in properworking order.

However, if the actual variation in the torque output by internalcombustion engine 1 is greater than the maximum permissible variation inoutput torque, an error has occurred and an error signal F is generated.

This error may be due to the fact that the sensors involved incontrolling and/or regulating internal combustion engine 1 aremalfunctioning. In particular, it means that variations in the outputsignals have occurred in one or more of the sensors, for example, due toaging or other phenomena.

However, it is also possible that the control unit is no longer inproper working order in the above-mentioned error situation and hasproduced the error.

In each case, error signal F generates, for example, a correspondingindication for the driver in the above-mentioned error situation, orother actions can be taken to correct the error.

What is claimed is:
 1. A method for detecting an error when operating aninternal combustion engine, comprising the steps of: at least one ofcontrolling and regulating output power by an internal combustion engineas a function of performance qualities of the internal combustion engineand a driver request; independently of the step of at least one ofcontrolling and regulating, determining a permissible variation in theoutput power over a predetermined period of time and an actualvariation, in the output power over a corresponding predetermined periodof time, and comparing the permissible variation to the actualvariation; and generating an error signal indicating a sensor error as afunction of the comparison.
 2. The method according to claim 1, wherein:the internal combustion engine is for a motor vehicle.
 3. The methodaccording to claim 1, further comprising the step of: determining thepermissible variation in the output power as a function of the driverrequest.
 4. The method according to claim 3, wherein: the driver requestincludes a variation in position of an accelerator.
 5. The methodaccording to claim 1, further comprising the step of: determining thepermissible variation in the output power as a function of a speed ofthe internal combustion engine.
 6. The method according to claim 1,further comprising the step of: determining the actual variation of theoutput power as a function of at least one of an oxygen content ofemitted exhaust gas and an intake air flow.
 7. The method according toclaim 1, further comprising the step of: taking a delay into account,comparing the permissible variation in the output power to the actualvariation in the output power.
 8. The method according to claim 1,further comprising the step of: generating the error signal if theactual variation in the output power over the predetermined period oftime is greater than the permissible variation in the output power overthe predetermined period of time.
 9. The method according to claim 1,further comprising the step of: converting the performance quantities ofthe internal combustion engine into torques.
 10. The method according toclaim 9, wherein: the torques include a permissible variation in atorque output by the internal combustion engine and an actual variationin the torque output by the internal combustion engine.
 11. An internalcombustion engine having a control unit for detecting an error whenoperating the internal combustion engine, the control unit: one ofcontrolling and regulating output power of the internal combustionengine as a function of performance quantities of the internalcombustion engine and a driver request; determining, independently of atleast one of the control and the regulation of the output power, apermissible variation in the output power over a predetermined period oftime and an actual variation in the output power over a correspondingpredetermined period of time; comparing the permissible variation of theoutput power to the actual variation of the output power; and generatingan error signal indicating a sensor error as a function of thecomparison.
 12. The internal combustion engine according to claim 11,wherein: the internal combustion engine is for a motor vehicle.
 13. Amethod for detecting an error when operating an internal combustionengine of a motor vehicle, comprising: determining a permissiblevariation in output power of an internal combustion engine of a motorvehicle over a predetermined period of time and an actual variation inthe output power over a corresponding predetermined period of time, andcomparing the permissible variation to the actual variation; andproviding an indication of a sensor error as a function of thecomparison.
 14. The method according to claim 13, further comprising:independently of the indicating step, one of controlling and regulatingoutput power of the internal combustion engine as a function ofperformance quantities of the internal combustion engine and a driverrequest.